Accumulating over-under conveyors are well known. These conveyors use chain loops that form tracks for supporting pallets that ride along tracks. The pallets have shoes for engaging the chain loops that form upper and lower tracks. The shoes engage the outside of the chain loop when traveling along the upper track, and the inside of the chain loop when traveling along the lower track. Examples of some over/under conveyor designs are disclosed in U.S. Pat. Nos. 5,495,933 and 5,407,058. These conveyor designs use two loops of triple roller strand conveyor chain that pass around sprocket assemblies. The head sprocket assembly includes a drive sprocket wheel. A series of pallets are positioned atop an upper segment of the chain loops. In the '933 design, each drive sprocket assembly includes a pallet drive disc. Each pallet drive disc has a series of spaced radiused pockets recessed into the perimeter of the disc to form a positive drive. The '058 design has a split disc gripper mechanism and tapered gripper bar to provide a friction drive in lieu of the positive drive. A pallet return that includes tapered ride bars and split disc gripper mechanisms is provided at the conveyor ends to swing the pallet down around sprockets and onto the lower return run, and then swing the pallets up onto the upper or advancing run. In these designs, the pallets can be linked into a pallet assembly to allow the conveyor to be used with larger work pieces. The pallets have a linking bar received over self-aligning bearings mounted on a roller mounting bolt.
A problem with conventional over/under conveyor designs is the vertical height require by the conveyor to invert their pallets or work platforms. For example, the '933 and '058 designs use individual pallets that are twelve (12) inches long. These long rigid pallets lift high and swing wide around both the drive and driven shafts. Although the pallets are linked, the conveyor still requires at least 18 inches of clearance from the floor to the centerline of its drive shafts. Yet, higher clearances can make it more difficult to load and unload the conveyer, particularly when bulky, heavy or awkward workpieces are being moved.
Another problem with conventional conveyors is they require precise alignment, particularly with respect to the pallet or work platform inversion mechanisms at the ends of the conveyor. For example, the '058 design requires highly machined and complicated components, such as split disc tapered gripper mechanisms. The '933 design requires a precise alignment of components parts. Slight misalignments and normal wear and tear can jam the conveyers and result in costly shut downs. Jamming is particularly troublesome with positive engagement inversion systems like the '933 deign which can bind and jam during use. Conveyor shut downs are particularly problematic because they can negatively impact an entire manufacturing operation.
Another problem with conventional over/under conveyor designs is the complexity of their design. The designs include many components that can break or jam during operation. The designs are also costly to manufacture and service.
The present invention is intended to solve these and other problems.